1. Field of the Invention
The present invention relates to a reducer of an electronic power steering apparatus, and more particularly to a reducer of an electronic power steering apparatus that aids the operation of a steering wheel by the driver by preventing a clearance from being caused by frictional wear between a worm and a worm wheel, by reducing rattle noise caused by backlash, and by minimizing the change in the clearance due to a change in torque.
2. Description of the Prior Art
FIG. 1 is a schematic view of a conventional electronic power steering apparatus. As illustrated in FIG. 1, the electronic power steering apparatus 100 includes a steering system 130 extending from a steering wheel 102 to wheels 126 and an auxiliary power mechanism 140 providing auxiliary steering power to the steering system 130.
The steering system 130 includes a steering shaft 106 one side of which is connected to the steering wheel 102 to be rotated in conjunction with the steering wheel 102 and the opposite side of which is connected to a pinion shaft 108 by the medium of a pair of universal joints 104. The pinion shaft 108 is connected to a rack bar 112 though a rack and pinion mechanism 110, and opposite ends of the rack bar 112 are connected to the wheels 126 of the vehicle through tie rods 122 and knuckle arms 124.
The auxiliary power mechanism 140 includes a torque sensor 142 detecting a torque applied to the steering wheel 102 by the driver and outputting an electrical signal in proportion to the detected torque, an electronic control unit 144 generating a control signal based on the electrical signal transmitted from the torque sensor 142, a motor 146 generating auxiliary power based on the control signal transmitted from the electronic control unit 144, and a reducer 150 having a worm 152 and a worm wheel 156 to transmit the auxiliary power generated by the motor 146 to the steering shaft 106.
Accordingly, in the electronic power steering apparatus 100, the torque generated by the rotation of the steering wheel 102 is transmitted to the rack bar 112 via the rack and pinion mechanism 110, and the auxiliary power generated by the motor 146 due to the generated torque is transmitted to the rack bar 112.
That is, both the torque generated by the rotation of the steering wheel 102 and the auxiliary power generated by the motor 146 axially move the rack bar 112.
FIG. 2 is a sectional view illustrating the reducer of the conventional electronic power steering apparatus. As illustrated in FIG. 2, in the reducer 150, a worm 152 is formed on a worm shaft 254 and worm shaft bearings 257 are installed at opposite ends of the worm shaft 254 to support the worm shaft 254. A plug bolt 210 is coupled between a damping coupler 240 and one of the worm shaft bearings 257 to prevent the bearing 257 from being pushed in the axial direction of the worm shaft 254, and is fixed by a plug nut 220.
The worm shaft 254 is connected to the motor 146 by the medium of the damping coupler 240 to be rotated by the drive force of the motor 146.
The worm wheel 156 is formed on one side of the outer periphery of the worm 152 on the worm shaft 254 to enmesh the worm 152, and is mounted to the steering shaft 106 transmitting the rotational force of the steering wheel 102 operated by the driver so that the rotational force of the worm shaft 254 by the drive force of the motor 146 is transmitted to the steering shaft 106.
The gear housing 260 carries the worm 152 and the worm wheel 156 and the motor 146 transmitting a drive force to the worm shaft 254 is provided on one side of the gear housing 260. The motor 146 is coupled to the gear housing 260 by means of a motor cover 230 using a bolt 250.
Balls 258 are interposed between an inner race 280 and an outer race 270 of the worm shaft bearing 257 to support the rotation of the worm shaft 254 connected to the motor 146 at one end of the gear housing 260.
The reducer of the electronic power steering apparatus smoothly and stably maintains the steering operation of the driver by controlling drive of the motor using the electronic control unit of the vehicle according to the travel condition of the vehicle and by transmitting the rotational force of the worm shaft generated by the drive force of the motor in addition to the rotational force of the steering wheel operated by the driver.
However, in the reducer of the conventional electronic power steering apparatus, a clearance is caused by frictional wear between the worm rotated by the drive force of the motor and the worm wheel and rattle noise is generated by backlash.
This problem, in turn, hampers accurate transmission of the auxiliary steering force for aiding the operation of the steering wheel by the driver.